The same question has bedeviled some of history's greatest scientists. For example, in 1719 astronomer Edmund Halley collected accounts of a widely-observed fireball over England. Many witnesses, wrote Halley, "[heard] it hiss as it went along, as if it had been very near at hand." Yet his own research proved the meteor was at least "60 English miles" high. Sound takes about five minutes to travel such a distance, while light can do it in a fraction of a millisecond. Halley could think of no way for sky watchers to simultaneously hear and see the meteor.Baffled, he finally dismissed the reports as "pure fantasy" -- a view that held sway for centuries.